Ink drop printer charge compensation

ABSTRACT

Every other drop in an ink jet printer is charged for use in printing, and intervening drops are charged negatively with a charge proportional to the charge on the preceding drop.

United States Patent 1191 Chen 1 1 Sept. 3, 1974 INK DROP PRINTER CHARGE 3,631,511 12/1971 Keur et a1. 346/75 COMPENSATION r [75] Inventor: Winston H. Chen, Yestal, NY. Primary Examiner joseph w Hartary [73] Assignees International Business Machines Attorney, Agent, or Firm-Francis V. Giolma Corporation, Armonk, NY. [22 Filed: June 18, 1973 211 App]. No.: 370,884 57] ABSTRACT [52] US. Cl 346/1, 317/3, 346/75 Every other dr p in an k jet p t r is cha g d f r [51] Int. Cl. 60111 18/00 use in p ting, and int r ening drops are charged neg- 53 Fieldflf Search 346/75, 1; 317/3 atively with a charge Proportional to the charge on the 1 preceding drop. [56] References Cited UNITED STATES PATENTS 9 Claims, 7 Drawing Figures 3,562,757 2/1971 3 1318611661....-.,:..,.. 346/1 1 v 20 22 DATA DIGITAL T0 7 CONVERTER ,34 MM ANALOG 26 GATE . DlFF. {0 ,38 AMP;

, v Q 1 132 ANALOG 2 I 24 CLOCK 2 R3 CHAREING 4 ELECTRODE minnow w" I 3.833.910

' arm 10: 2

T= PERIOD OF DROP FORMATION DROP ubcdefg FIG. 2

DROPS DEFLECTED FOR PRINTING DROPS DEFLECTED FIG, 3 I TO CUTTER T EVERY 5RD. DROP USED FOR PRINTING I Va W FIG. 4

Vd Vu PAIENIEII st? 3mm mm a or 2 20 ,22 DATA DIGITAL T0 SOURCE ANALOG CL DROP CLOCK v DI 2 W DIGITAL I0 ANALOG DA CONVERTER OUTPUT 40 CHARGING VOLTAGE v OUTPUT 42 COMPENSTATING VOLTAGE v 44 TOTAL OUTPUT v m FIG. 7

1 INK DROP PRINTER CHARGE COMPENSATION FIELD OF THE INVENTION DESCRIPTION OF THE PRIOR ART US. Pat. No. 3,562,757 which issued on Feb. 9, 1971 to V. E. Bischoff discloses the use of uncharged guard drops between charged drops to reduce interaction between the charged drops.

U.S. Pat. No. 3,631,511 which issued on Dec. 28, 1971 to Robert I. Keur, et .al. discloses the method of compensating for the adverse effects of a just charged drop on a subsequent drop in an ink jet printer by modifying the charge placed on the following drop.

SUMMARY OF INVENTION This invention relates generally to ink jet printing and it has reference in particular to means for and a method of compensating for the adverse effects of a just charged drop on a following drop or drops.

More specifically this invention provides for controlling the interaction between successive charged drops in an ink jet printer by placing a negative charge on a discard drop between them.

Another object of the invention is to provide for utilizing a fractional portion of the clock pulses producing ink drops for placing charges on drops separated by one or more drops, and placing a negative charge on one of the intervening drops which is related to the charge on the preceding charged drop.

Yet another object of the invention is to provide for using both, pulses derived from a clock driving a drop forming transducer, and inverted clock pulses, for gating character generating signals to an operational amplifier connected to a drop charging electrode in an ink jet printer.

Still another object of the invention is to provide for dividing the clock pulses driving an ink drop transducer into half and using these pulses, directly with one gate,

and inverted with another gate, to operate an operational amplifier so as to charge alternate drops to form characters, and place negative charges on intervening drops to minimize'charge interaction effects.

Other objects, features, and advantages of the invention will be apparent from the following more particu lar description of a preferred embodiment of the invention as illustrated in the accompanying drawing.

' BRIEF DESCRIPTION OF THE DRAWING In-the drawing:

FIG. 1 is a schematic representation of a drop form ing nozzle and a charging electrode in an ink jet printer.

FIG. 5 shows a similar curve using every third drop and the other one of the intervening drops for charge compensation.

FIG. 6 is a schematic circuit diagram of a compensation control circuit according to the invention and used with the nozzle and charging electrode of FIG. 1; and

FIG. 7 shows characteristic curves of the various signals in the circuit of FIG. 6

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1 the reference numeral 10 denotes generally an ink jet printer drop charging system in which ink is emitted in a stream 12 under pressure from a nozzle 14 and passes through a cylindrical charging electrode 16 in which it breaks into separate drops designated a, b, c, d and e respectively. If the capacitance of the charging electrode jet system be C, then the induced charge on drop e at the moment of its separation from the stream is Q =C V if a, b, c, and d are uncharged drops. However if a, b, c, and d are charged drops, the induction resultsin (Equation I No. l) where C and C are the capacitance between drops d and e and between drops cand e; and K is a constant. The overshoot effect is inversely related to distance and therefore only the efi'ect of the adjacent two or three preceding drops has to be considered.

The present invention relates to the case in which every other drop or every third drop is used for printing. Assuming that we use every other drop for printing, say drops a, c, and e in FIG. I. In order to compensate for theovershoot effect on drop a from drop 0 we intentionally charge .drop d by v d 'Cce de c that. gives Q,, Cce/ de X QC As a result of this Q equation 1) becomes: Q, =CV +KC I Q +KC X Q -=CV,+O

higher order terms this approximates z CV The overshoot effect from drop c to the drop e, therefore is compensated for by that from the drop d to the drop e. InIthe same manner, the overshoot effect from drop a to drop 0 can be offset by charging drop b by i I b ac/ bc a Noticethat ab/Ch ue/Cu a is a constant and is the same for all drops in that sequence.

schematically, if every other-drop is used for printing, the basic charging voltages are as shown in FIG. 2, where Tis the period of drop formation.

With the present compensation scheme the charging voltages become modified as shown in FIG. 3 by the negative intervening compensating voltages V V and V; being respectively equal to -a X V,,, -a X V and a X V, respectively.

The same principle can be applied for the case in which every third or every fourth drop is used for printing if compensation is necessary. As shown in FIGS. 4 and 5 if the drops V and V are to be used for printing, a compensating voltage V .B X Va and V, B X V may be used on the drops following the drops charged to the voltages V, and V Likewise, as shown in FIG. 5 if the charging voltages V, and V,, are used to charge drops for printing, Charging voltages V and V, may be used which immediately precede the charging-voltages V, and V, with like effect.

Referring to FIG. 6 it will be seen that instead of merely connecting a data source 20 to a digital to analog converter 22 and thence to the charging electrode 24 in the normal manner for charging ink drops as shown in FIG. 2, a differential amplifier 26 may be connected between the digital to analog converter 22 and the charging electrode 24. A drop clock or oscillator 30 is connected by a divider 32 (which divides the clock pulse by two) to the data source 20 and to an analog gate 34 connected between the digital to analog converter 22 and the differential amplifier 26. An inverter 36 is connected between the divider 32 and a second analog gate 38, which is connected to the other input of the differential amplifier. By properly proportioning the resistors R1, R2, R3 and R4 the voltage applied to the charging electrode 24 may be made to conform to 'that shown in FIG. 3 with negative voltages properly proportional to the preceding voltage being applied between the positively applied drops. a

Referring to page 202, paragraph 6.1.1 Differential DC amplifiers using one operational amplifier in the publication Operational Amplifiers Design and Application by Burr-Brown Research Corporation, copyright nit in R1 1 5 I? Let V,/ V, where K a minus percentage.

' it follows that therefore 4 IfT .30 then Values of K 0.03 to 0.30 have been found satisfactory.

Referring to FIG. 7 it will be seen that if the clock 20 has an output frequency on the order of KHz which is within the range of 5-200 KHz disclosed in U.S. Pat. No. 3,298,030 which issued on Jan. l0, 1967 to A. M. Lewis, et al. represented by the curve CL then the output of the divider 32 will be represented by the curve DI. With the digital to analog-converter 22 output Vin comprising successively increasing 10 volt steps represented'by the curve DA, the output charging voltage V, from the analog gate 34 comprises a plurality of successively increasing 10 volt steps and will be represented by the curve 40, and the compensating voltage output V comprising negative step signals on the order of one fourth of the value of the preceding V, signal, is represented by the curve 42 from the analog gate 38. The resultant voltage V, applied to the charging electrode 24 will be represented by the curve 44 having successively increasing 10 volt positive steps and successively increaseing 2.5 volt negative steps therebetween.

While the invention has been described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed isi i 1. A method of drop charge compensation in an ink drop printer comprising the steps of i charging spaced apart drops with positive data sig- 'nals, leaving at least one other drop between each data signal charged drop, and 1 y I charging said other drops with a charge proportional to but of the opposite polarity ofthe charge on a preceding signal charged drop to negative the effect of one positively charged data signal drop on an adjacent positively charged data signal drop.

2. The method of drop charge compensation in an ink drop printer which comprises the steps of producing ink drops at predetermined spaced intervals, v charging selected ones of said ink drops which are separated by at least one intervening drop, with data signals for printing, and v charging at least one of said intervening drops between each pair of data signal charged drops with a charge proportional to but of the opposite polarity of the preceding one of said data signal charged drop, to negative the effect of said one data signal charged drop on an adjacent data signal charged drop.

3. In an ink drop printer having a nozzle for producing a stream of ink drops,

transducer means associated with said nozzle for producing varicosities in said stream to insure uniform drop formation,

clock means for applying timed pulses to said transducer means,

a charging electrode positioned in spaced relation with said nozzle for charging selected ones of said drops,

deflection means providing a field to deflect said charged drops,

and means connecting said charging electrode to a source of data signals,

the improvement comprising circuit means connected between said charging electrode, and said source of data signals and said clockmeans to charge selected spaced apart drops from said source for printing and other drops between said 5 by said circuit means including a digital to analog converter and an operational amplifier connected to effect energization of said charging electrode from said source.

S. The invention as defined in claim 4 characterized by said circuit means including gate means connecting said converter and said clock means to said amplifier.

6. The invention as defined in claim 5 characterized by said circuit means including an inverter connecting said clock means to one of said gate means.

7. The invention as defined in claim 3 characterized by said circuit means including means dividing said clock pulses connecting said clock means to said gate means.

8. The invention as defined in claim 3 characterized by said dividing means reducing said clock pulses by one-half.

.9. The invention asdefined inclaim 3 characterized by said dividing means reducing said clock pulses by two-thirds. 

1. A method of drop charge compensation in an ink drop printer comprising the steps of charging spaced apart drops with positive data signals, leaving at least one other drop between each data signal charged drop, and charging said other drops with a charge proportional to but of the opposite polarity of the charge on a preceding signal charged drop to negative the effect of one positively charged data signal drop on an adjacent positively charged data signal drop.
 2. The method of drop charge compensation in an ink drop printer which comprises the steps of producing ink drops at predetermined spaced intervals, charging selected ones of said ink drops which are separated by at least one intervening drop, with data signals for printing, and charging at least one of said intervening drops between each pair of data signal charged drops with a charge proportional to but of the opposite polarity of the preceding one of said data signal charged drop, to negative the effect of said one data signal charged drop on an adjacent data signal charged drop.
 3. In an ink drop printer having a nozzle for producing a stream of iNk drops, transducer means associated with said nozzle for producing varicosities in said stream to insure uniform drop formation, clock means for applying timed pulses to said transducer means, a charging electrode positioned in spaced relation with said nozzle for charging selected ones of said drops, deflection means providing a field to deflect said charged drops, and means connecting said charging electrode to a source of data signals, the improvement comprising circuit means connected between said charging electrode, and said source of data signals and said clock means to charge selected spaced apart drops from said source for printing and other drops between said selected drops with a charge proportional to but of the opposite polarity of that of a preceding selected drop.
 4. The invention as defined in claim 3 characterized by said circuit means including a digital to analog converter and an operational amplifier connected to effect energization of said charging electrode from said source.
 5. The invention as defined in claim 4 characterized by said circuit means including gate means connecting said converter and said clock means to said amplifier.
 6. The invention as defined in claim 5 characterized by said circuit means including an inverter connecting said clock means to one of said gate means.
 7. The invention as defined in claim 3 characterized by said circuit means including means dividing said clock pulses connecting said clock means to said gate means.
 8. The invention as defined in claim 3 characterized by said dividing means reducing said clock pulses by one-half.
 9. The invention as defined in claim 3 characterized by said dividing means reducing said clock pulses by two-thirds. 